The disclosure according to the present disclosure relates to a speed change device that includes a first clutch and a second clutch disposed around the first clutch.
There has hitherto been known a speed change device that includes a clutch C3 constituted as a multi-plate friction hydraulic clutch and a clutch C4 constituted as a multi-plate friction hydraulic clutch and disposed on the inner side of the clutch C3 (see Japanese Patent Application Publication No. 2013-155849, for example). The clutches C3 and C4 of the speed change device share a drum member that includes an inner drum and an outer drum that has a base end portion welded to the outer periphery of a sidewall portion of the inner drum. The outer drum of the drum member defines an engagement oil chamber of the clutch C3 together with a piston of the clutch C3. In addition, the inner drum of the drum member has an inner tubular portion that supports a piston of the clutch C4 and a cancel plate, an annular sidewall portion extended radially outward from one end of the inner tubular portion, and a short cylindrical fixation portion extended from the sidewall portion on the inner side with respect to a joint portion with the outer drum. The clutch drum of the clutch C4 and the cancel plate which defines a centrifugal hydraulic pressure cancellation chamber of the clutch C3 are fastened to the fixation portion of the inner drum via a rivet. Further, the piston of the clutch C4 has an extended portion that is in sliding contact with the inner peripheral surface of the fixation portion of the inner drum through a seal member, and an engagement oil chamber of the clutch C4 is defined on the radially inner side of the inner peripheral surface of the fixation portion.